1. Field Of The Invention
This invention relates to nonwoven felt-like products of filamentary polytetrafluoroethylene (hereinafter referred to as PTFE).
2. Description Of The Prior Art
The formation of felts from polymeric filamentary materials is taught in Lauterbach U.S. Pat. No. 2,910,763 issued Nov. 3, 1959. The use of such felts for filtering is taught in Lauterbach U.S. Pat. No. 2,933,154 issued Apr. 19, 1960. Felt-like products of PTFE have become commercial products and are used in filtration.
The use of PTFE felts as high efficiency and high porosity filters particularly useful as filters for the removal of fine particles such as fly ash from gaseous combustion products of coal fired furnaces and boilers is shown in Fagan U.S. Pat. No. 4,031,283 issued June 21, 1977.
To meet new stringent regulations, filters which are more efficient, have a low level of leakage of particles, are cleanable and are resistant to blinding are required. However, porosity of the filters must still be high to maintain the air pressure drop across the filter at a very low level. Also, the air/filter cloth, i.e., the ratio of volume of air which passes through an area of the filter, must be at a high level.